1. Field of the Invention
The present invention relates to a mobile terminal, a circuit board, a circuit board design aiding apparatus and method, a design aiding program, and a storage medium having stored therein the design aiding program. More particularly, the present invention relates to a tamper-resistant circuit board, an apparatus and method for aiding the design of the circuit board, a computer-readable storage medium having stored therein the program for performing the method, and a mobile terminal containing the circuit board.
2. Description of the Background Art
In recent years, with the development of digital information technologies and the explosive popularization of digital information communication infrastructure, it has become more common to process content such as music, images, video, and games, as digital information. The content converted into digital information is vulnerable to fraudulent acquisition by communications interception, wiretapping, spoofing, or the like, and fraudulent activities such as illegal copies and illegal modification of storage media having stored therein the data of the content. Thus, it is a great challenge to establish security systems for protecting the rights of content copyright holders and the profits of content distributors. Accordingly, techniques are required which protect copyrighted works converted into digital information. Note that in the following description, the difficulty of gaining unauthorized access to confidential information, such as content and signals, is referred to as “tamper resistance”.
For security techniques for improving tamper resistance by communication media, there have been various known techniques. In most of the techniques, tamper resistance is improved by identifying authorized systems or encrypting data using encryption/authentication techniques. A representative of the techniques includes a challenge-response mutual authentication technique in which upon accessing a confidential-data storage region where confidential data which requires the protection of copyrighted works is stored, random numbers and response values are exchanged between apparatuses to mutually authenticate each other's validity and only a valid access is permitted. In communication of confidential data, encryption communication is performed which uses random numbers or response values for mutual authentication, thereby preventing unauthorized decoding.
One of the conditions for improving the tamper resistance of a circuit board in which components and the like are installed and connected by wiring, is the difficulty of probing a signal line which transmits digital information. This is because the information converted into a digital signal can be easily reproduced with the same quality as the original only if the signal is probed and the logic of the signal is determined. The harder it is to read a signal on the circuit board, i.e., the harder it is to perform probing, the harder it gets to analyze or copy digital information by external unauthorized access, and the easier it is to perform probing, the easier it gets to extract a signal, and thus it becomes easy to analyze or copy digital information.
For security techniques for circuit boards, there have also been various known techniques. For example, there is a technique in which the circuit section where confidential information is processed is formed in a one-chip IC format so that a signal of the confidential information cannot flow on the circuit board. In addition, there is a technique in which the circuit section where confidential information is processed is covered by a resin or the like. Further, there is a technique in which a component is arranged to cover a probeable portion of a signal line through which a signal of confidential information flows (see Japanese Laid-Open Patent Publication No. 2002-299842).
However, in the method in which the circuit section where confidential information is processed is formed in a one-chip IC format or covered by a resin or the like, problems arise that off-the-shell ICs cannot be used, all the chips and wiring on the circuit board need to be taken care of, and the like. Thus, such methods are impractical in terms of the current techniques and manufacturing costs. In addition, after the circuit section is formed in a one-chip IC format or covered by a resin, not only third parties but also a developer or designer (hereinafter referred to as a “designer or the like”) is unable to verify a confidential signal. Further, to adopt conventional encryption/authentication techniques for communication in circuit boards, a logic for realizing the techniques needs to be incorporated in all LSIs handling digital information. Thus, the adoption of such techniques is also impractical in terms of the current techniques and manufacturing costs. Moreover, the method in which a signal line for confidential information is covered by a component, as in the case of Japanese Laid-Open Patent Publication No. 2002-299842, is problematic because probing can be easily done by removing the component. As described above, with the conventional techniques, it is very difficult to completely conceal a signal line of the circuit board, through which confidential information flows.